1. Field of the Invention
The present invention relates to a hub unit mounting structure.
2. Related Art
A drive wheel supporting rolling bearing device is configured such that an axle (a drive shaft) is spline fitted in a central shaft hole in a hub wheel from an inner side of a vehicle, so that the axle and the hub wheel rotate together.
To describe specifically, the axle is formed diametrically large at a body portion and diametrically small at a distal end side thereof, and a spline is formed on a root side of the small-diameter portion of the axle, while a threaded portion is formed on the distal end side thereof, whereby a hub receiving surface of a vehicle outer side end face of the large-diameter portion of the axle is brought into abutment with a vehicle inner side end face of an inner ring by spline fitting the axle in the shaft hole in the hub wheel. Then, a nut is screwed on the threaded portion at the distal end of the axle so as to be pressed against a vehicle outer side end portion of the hub wheel, so that the hub wheel and the inner ring are held axially by the nut so screwed and the hub receiving surface, whereby the hub wheel, the axle and the inner ring are integrated together.
By the configuration that has been described above, normally, the axle, the hub wheel and the inner ring rotate together as an integrated unit. In conditions where a vehicle is drastically started or turned, however, the axle is twisted and a slip occurs between contact surfaces of the inner ring and the end face of the large-diameter portion of the axle, whereby a stick-slip noise (a so-called clink noise) is generated.
As a countermeasure against this, the tightening force of the nut is increased to increase, in turn, the frictional force at the vehicle inner side end face of the inner ring so that no slip is generated between the contact surfaces of the inner ring and the end face of the large-diameter portion of the axle. Alternatively, a lubricant is applied to the vehicle inner side end face of the inner ring to thereby, on the contrary, decrease the frictional force between the contact surfaces so as to release the twist generated in the axle on an early occasion.
Furthermore, according to JP-A-2005-75067, in order to effectively prevent the generation of the stick-slip noise, by bringing a non-wheel side of a connecting portion of an axle where the axle connects to a hub wheel nearer to an abutment spot between an end face side of an inner ring and a large-diameter portion of the axle, a difference in torsional rigidity of the axle between the abutment sport and a connecting spot on the non-wheel side of the connecting portion is made small.
When the tightening force of the nut is increased, however, there has been caused a problem with the strength of the threads, and with the application of the lubricant, there has been caused a problem that the effect of the lubricant does not last long. In addition, with JP-A-2005-75067, a change in structure of both the hub unit and the axle is entrained.